In various applications involving large roller bearings it makes sense to have available an ultrasonic testing device that allows non-destructive detection of defects in the material with no need to dismantle the bearing. This is especially true of the large roller bearings employed as rotary joints in offshore cranes.
European Patent A 1 228 731 proposes providing at least one opening in at least one ring to accommodate an ultrasonic probe. Material defects in the other ring are then detected by way of a contact surface in that ring. One drawback of this system is that the ultrasonic probe must be positioned in the vicinity of the races. At least some of the lubricant must accordingly be removed from that vicinity and the contact surface must at least to some extent be cleaned. Furthermore, any worn-off particles that accumulate in the area can contaminate the results. Again, once the bearing has been used for a while, the permissible wear will increase play. The increased play will shift the contact surface in relation to the ultrasonic probe, which can also lead to errors in measurement.